There's absolutely nothing wrong with the celebration of good looks every now and then. And a little digital self-affirmation never hurt anyone.
We all appreciate a like or fifty on Instagram for those selfies we've imported using Snapchat filters, and you'll probably agree that some selfies require a little more work than others before you can reap the rewards.
Think ambiance, lighting and setting. And depending on when and where you take your selfie, onlookers may make you feel a bit uncomfortable.
The only reason I stop is because I automatically feel like I'm going to be judged and misconstrued as this vain, "too self-obsessed to observe the world around her" kind of girl.

You feel uncomfortable because society has developed a habit of looking down on women who engage in constant self-documentation.
So unlike a previous study conducted by Psychology Today in 2015 that suggested that spending a lot of time on social media is associated with high levels of narcissism and self-objectification, their latest research looked at the correlation between narcissism and selfie-taking, yielding a less disapproving result.
This research revealed that narcissism isn't actually the sole motive for posting selfies on an almost daily basis, but rather that selfie culture is just a fun way of contributing to social media, while also cultivating an image for yourself.
However, people still tend to vilify selfie enthusiasts. Bizarre. Why should I be judged for using my own data to post a picture my own face on my own social media account?
That said, I have found myself in a few situations where taking a selfie is tricky and should, perhaps, rather be avoided: 

In an elevator

The possibilities are endless when you walk into an empty lift - you can do anything from adjusting your bra strap to taking a selfie. That is until the lift stops on the next floor to let seven people in and you suddenly have to act all nonchalant and normal.
So I'd say rather avoid, unless you're travelling up or down the elevator during hours there are very few people around. 

Great lighting, bad background.

This happens when you've done your makeup really well and the natural light gods are on your side, but the rest of the setting is just really off. In this scenario there's either a pile of dirty dishes behind you, a very messy bedroom or an unavoidable photobomb waiting to happen. 
Rather opt out of the selfie taking because posting a less than stellar picture of your environment will just ruin the entire aesthetic of your Instagram feed. Remember, we're cultivating identities here.

Your work desk

Another perfect opportunity to show off your great makeup because sometimes (only sometimes) the fluorescent lights in the office hit all the right spots on your face, but rather avoid the urge to self-snap for productivity's sake. 
Or you do anyway, but clandestinely with your phone at keyboard level so passersby (including your boss) don't notice.

Funerals

Using social media during serious events can end up trivialising such moments. 
If you're paying your respects to a deceased family member or close friend, it's probably best not to make the day about how good you look.

Graduation stage

Yes, you're sitting on stage behind highly-esteemed chancellors, academic doctors and professors, so you probably don't want to seem like a disruptive child with your forearm in the air while an honorary doctorate recipient is making a speech.